The Homeland Security Department is adding three surveillance drone aircraft to a domestic fleet chiefly used to patrol the border with Mexico even though officials acknowledge they don't have enough pilots to operate the seven Predators they already possess.

The new drones are being purchased after lobbying by members of the so-called drone caucus in Congress, many from districts in Southern California, a major hub of the unmanned aircraft industry, says an LA Times report.

Officials said the Customs and Border Protection Office of Air and Marine, which operates the drones, has enough pilots to fly the current fleet only five days a week, the report says.

Every unmanned aircraft requires not just a ground-based pilot, but a platoon of surveillance analysts, sensor operators and a maintenance crew, the report says.

Homeland Security officials say they ultimately hope to deploy 18 to 24 drones along the borders. For now, however, they say that they must shift money from other programs to buy the satellite bandwidth required to fly the seven drones they use.